Micro light-emitting diode display device

This application claims the priority benefit of Taiwan application serial no. 110130934, filed on Aug. 20, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

The disclosure relates to a display device, and in particular relates to a micro light-emitting diode display.

Multiple pixels in a micro light-emitting diode display may be formed by disposing multiple semiconductor light-emitting mesas on a semiconductor connection layer. Each of the semiconductor light-emitting mesas corresponds to a sub-pixel, and is arranged on the semiconductor connection layer in the form of an array. In addition to being the connection layer, the semiconductor connection layer may also serve as the common electrode of each of the light-emitting mesas, and is electrically connected to the circuit substrate through the bonding metal layers.

However, the resistance value of the semiconductor connection layer is higher than that of a conductor. The number of recombining electron-hole pairs is lower for the light-emitting mesas that are farther away from the common ground point. In contrast, the number of recombining electron-hole pairs is higher for the light-emitting mesas that are closer to the common ground point. Therefore, the brightness of the micro light-emitting diode display may be nonuniform.

The disclosure provides a micro light-emitting diode display device having uniform light-emitting brightness.

According to an embodiment of the disclosure, a micro light-emitting diode display device including a circuit substrate, an epitaxy structure and a conductive layer is provided. The epitaxy structure is electrically connected to the circuit substrate, and includes a connection layer and a plurality of light-emitting mesas. The light-emitting mesas are disposed on the connection layer, wherein a thickness of the connection layer is less than a thickness of the light-emitting mesas, and the connection layer has a first surface exposed by the light-emitting mesas and a second surface opposite to the first surface. The conductive layer is disposed on the second surface of the connection layer and exposes a plurality of sub-areas of the second surface, wherein a vertical projection of the conductive layer onto the connection layer overlaps a vertical projection of the first surface onto the connection layer.

According to another embodiment of the disclosure, a micro light-emitting diode display device including a circuit substrate, an epitaxy structure and a transparent conductive layer is provided. The epitaxy structure is electrically connected to the circuit substrate, and includes a connection layer and a plurality of light-emitting mesas. The light-emitting mesas are disposed on the connection layer, wherein the connection layer has a first surface exposed by the light-emitting mesas and a second surface opposite to the first surface. The transparent conductive layer is disposed on the second surface of the connection layer, wherein the transparent conductive layer completely covers the second surface.

Based on the above, in the micro light-emitting diode display device provided by the embodiments of the disclosure, the conductive layer is disposed on the connection layer of the epitaxy structure. Since the resistance value of the conductive layer is less than the resistance value of the connection layer, the current of the circuit substrate may be transmitted more evenly through the conductive layer. In this case, for the light-emitting mesas with different distances from the common ground point, the same potential difference may drive the same number of recombining electron-hole pairs, which may prevent the micro light-emitting diode display device from having nonuniform brightness. In addition, as the resolution requirements become higher, the arrangement of the light-emitting mesas (sub-pixels) becomes denser. In contrast with the conventional situation in which the conductive layer is disposed on the first surface of the connection layer, the conductive layer of the disclosure is disposed on the second surface, which greatly improves the yield.

In order to make the above-mentioned features and advantages of the disclosure comprehensible, embodiments accompanied with drawings are described in detail below.

Referring toand, a micro light-emitting diode display devicehas a display area Aand a non-display area A, and includes a circuit substrate C, an epitaxy structure ES, and a conductive layer. The display area Arefers to an area in which a plurality of display sub-pixels PX are disposed, and the non-display area Ais disposed at least partially around the display area Aand may be an area in which a plurality of driving elements (not shown) are disposed. Each of the display sub-pixels PX has a light-emitting mesato provide image light of the micro light-emitting diode display device.

The epitaxy structure ES includes a connection layerand a plurality of light-emitting mesas. As shown in, a plurality of light-emitting mesasrespectively corresponding to a plurality of display sub-pixels PX are disposed on the connection layer, and each of the light-emitting mesasincludes a first-type semiconductor layer, a second-type semiconductor layer, and a light-emitting layer, wherein the light-emitting layeris a multiple quantum well (MQW). The connection layeris disposed on a plane parallel to the plane formed by the first direction Dand the second direction D, and has a first surfaceexposed by the light-emitting mesas, and a second surfaceopposite to the first surface.

According to an embodiment of the disclosure, the connection layeris an n-type semiconductor, the first-type semiconductor layeris an n-type semiconductor, and the second-type semiconductor layeris a p-type semiconductor, but the disclosure is not limited thereto. In another embodiment of the disclosure, the connection layeris a p-type semiconductor, the first-type semiconductor layeris a p-type semiconductor, and the second-type semiconductor layeris an n-type semiconductor. In particular, the connection layerand the first-type semiconductor layermay be integrally formed, that is, the two are the same layer. For example, through an etching process, the plurality of separated first-type semiconductor layersand the continuous connection layerare formed, which may increase the yield of mass transfer to the circuit substrate C, and use the connection layeras a common electrode to reduce power consumption.

The circuit substrate Cmay be, for example, a complementary metal-oxide-semiconductor (CMOS) substrate, a liquid crystal on silicon (LCOS) substrate, a thin film transistor (TFT) substrate, or other substrates with working circuits, which are not limited thereto. As shown in, the epitaxy structure ES is electrically connected to the circuit substrate Cthrough the bonding metal layer, the bonding metal layer, the bonding metal layer, and the bonding metal layer, wherein the bonding metal layerand the bonding metal layerare the common ground point.

When a voltage is applied to a bonding metal layervia the circuit substrate Csuch that a potential difference is present between the bonding metal layerand the common ground point, the potential difference generates a current, and the electron-hole-pair recombination occurs in the light-emitting mesaconnecting the bonding metal layerto which the voltage is applied, thereby generating light. The light emitted by the light-emitting mesaexits the micro light-emitting diode display devicealong a direction substantially parallel to a third direction D, and enters the eyes of the user, wherein the first direction D, the second direction D, and the third direction Dare perpendicular to one another.

Since the connection layerserving as the common electrode is a semiconductor, its resistance value is higher than that of a conductor. When a predetermined potential difference is applied to the common ground point and the bonding metal layerfarther away from the common ground point, the number of the recombining electron-hole pairs in the corresponding light-emitting mesais lower. When the same potential difference is applied to the common ground point and the bonding metal layercloser to the common ground point, the number of the recombining electron-hole pairs in the corresponding light-emitting mesais higher. In order to avoid the above situation, the conductive layeris disposed on the second surfaceof the connection layer, and the thickness of the connection layerin the third direction Dis configured to be less than the thickness of the light-emitting mesa, so as to utilize the conductive layerwith lower resistance to assist in transmitting the current, such that the current may be evenly distributed. Even if the same potential difference is applied to the common ground point and the bonding metal layerthat is farther away from the common ground point. the number of the recombining electron-hole pairs in the corresponding light-emitting mesais not lower. The light emitted from the light-emitting mesais prevented from being reflected in the interior of the connection layer. Light loss is avoided. Therefore, the light-emitting mesasof the micro light-emitting diode display devicemay have the same brightness when same potential differences are applied thereto, and the micro light-emitting diode display devicemay have good brightness uniformity.

When the area of the conductive layeris larger, the current is more evenly distributed, and the brightness uniformity of the micro light-emitting diode display deviceis better. If the vertical projection of the conductive layeronto the connection layeris a first projection, and the vertical projection of the first surfaceonto the connection layeris a second projection. in one embodiment, the area of the overlapping portion of the first projection and the second projection is greater than or equal to 0.5 times the area of the second projection. In one embodiment, the vertical projection of the first surfaceonto the connection layer(i.e., the second projection) completely falls within the vertical projection of the conductive layeronto the connection layer(i.e., the first projection). In another embodiment, the vertical projection of the first surfaceonto the connection layer(i.e., the second projection) completely falls within the vertical projection of the conductive layeronto the connection layer(i.e., the first projection), and the area of the overlapping portion of the first projection and the second projection is equal to the area of the second projection.

In this embodiment, the conductive layeris an opaque high-conductivity material, such as gold, titanium, aluminum, silver, platinum, and alloys thereof. Therefore, the conductive layeris configured to expose a plurality of sub-areasS of the second surface, and the sub-areasS respectively correspond to the light-emitting mesas. Specifically, as shown in, the vertical projections of the sub-areasS onto the connection layerrespectively overlap the vertical projections of the light-emitting mesasonto the connection layer, such that the light emitted by each of the light-emitting mesasmay penetrate the corresponding sub-areaS and then exit the micro light-emitting diode display device. The vertical projection of the conductive layeronto the connection layeroverlaps the vertical projection of the first surfaceonto the connection layerand does not overlap with the vertical projection of the light-emitting mesasonto the connection layer, but the disclosure is not limited thereto. In an embodiment of the disclosure, the vertical projection of the conductive layeronto the connection layerpartially overlaps the vertical projections of at least a part of the light-emitting mesasonto the connection layer. In other words, the areas of vertical projection of at least a part of the sub-areasS onto the connection layeris smaller than the areas of vertical projection of the corresponding light-emitting mesasonto the connection layer. Under such a configuration, the light emitted by the light-emitting mesasis further restricted by the conductive layer, and the light travels in a more concentrated direction, which avoids crosstalk between the display sub-pixels PX. Preferably, the ratio between the vertical projections of at least a part of the sub-areasS onto the connection layerand the vertical projections of the corresponding light-emitting mesasonto the connection layeris between 0.5 and 1, and if the ratio is less than 0.5, the light extraction rate may be insufficient.

Further, since the conductive layeris an opaque high-conductivity material, its thickness is configured to be less than or equal to the thickness of the epitaxy structure ES, so as to reduce the amount of light absorbed by the conductive layer. It should also be noted that the total area of the conductive layerdisposed in the display area Ais larger than the total area of the conductive layerdisposed in the non-display area A, so as to ensure that the current can be transmitted more evenly in the conductive layerof the display area A. Each of the light-emitting mesashas the same brightness when the same potential difference is applied thereto.

In this embodiment, the micro light-emitting diode display devicefurther includes a semiconductor pad, wherein the semiconductor pad, and the bonding metal layers,serving as the common ground point, are all disposed in the non-display area A, and the light-emitting mesasare disposed in the display area A.

The semiconductor padand the light-emitting mesasmay be fabricated in the same process and have similar structures. Since the top surfaces of each light-emitting mesaand the semiconductor padon the side away from the connection layeris coplanar, the yield of the process for respectively bonding the bonding metal layerand the bonding metal layeron the circuit substrate Cto the bonding metal layerand the bonding metal layercan be improved. Further, the bonding metal layerhas an epitaxial sectionE, such that the bonding metal layermay be electrically connected between the connection layerand the bonding metal layer.

In order to fully illustrate the various embodiments of the disclosure, other embodiments of the disclosure are described below. It is to be noted that the following embodiments use the reference numerals and a part of the contents of the above embodiments, and the same reference numerals are used to denote the same or similar elements, and the description of the same technical contents is omitted. For the description of the omitted part, reference may be made to the above embodiments, and details are not described in the following embodiments.

Referring toand, a micro light-emitting diode display devicehas a display area Aand a non-display area A, and includes a circuit substrate C, an epitaxy structure ES, and a conductive layerA. A plurality of light-emitting mesasare grouped into multiple light-emitting mesa groupsG in units of four light-emitting mesas, and the conductive layerA is configured to expose a plurality of sub-areasG of the second surface, wherein the sub-areasG respectively correspond to the light-emitting mesa groupsG. However, the disclosure is not limited thereto. In some embodiments, the light-emitting mesasof the micro light-emitting diode display deviceare grouped into a plurality of light-emitting mesa groupsG in units of at least three light-emitting mesas. When the color conversion elements (not shown, such as quantum dots) are subsequently disposed on the second surfacecorresponding to the at least three light-emitting mesas, the at least three light-emitting mesasmay respectively emit red light, green light and blue light, and form a full-color display device.

Similar to the micro light-emitting diode display device, the total area of the conductive layerA disposed in the display area Aof the micro light-emitting diode display deviceis larger than the total area of the conductive layerA disposed in the non-display area A, to ensure that the current may be transmitted more evenly in the conductive layerA of the display area A. Each of the light-emitting mesashas the same brightness when the same potential difference is applied thereto.

Referring to, a micro light-emitting diode display devicehas a display area and a non-display area, and includes a circuit substrate C, an epitaxy structure ES, a conductive layerB, a conductive layer, and an insulating layer. The conductive layerB includes a conductive layerBdisposed in the display area and a conductive layerBdisposed in the non-display area.

A width of the conductive layerBdecreases in the direction away from the second surface(i.e., along the positive direction of the third direction D), and the conductive layerBshows a bottom wide and top narrow view. The cross-sectional view of the conductive layerBshown inhas a conical shape, such that the light emitted by the corresponding light-emitting mesasmay be reflected and concentrated more toward the center. When the color conversion elements (not shown, such as quantum dots) are subsequently disposed on the second surfacecorresponding to the light-emitting mesas, the grooves G formed in the conductive layerBprovide the accommodation spaces having larger machining allowance for the color conversion elements disposed therein. In other embodiments, the width of the conductive layerBdecreases in a direction away from the second surface, and the conductive layerBhas a trapezoidal shape in a cross-sectional view.

The conductive layerBin the non-display area is also disposed in a through holeH penetrating the connection layerto electrically connect to the bonding metal layer, the bonding metal layerand the circuit substrate C. The current from the circuit substrate Cis sequentially transmitted to the bonding metal layer, the bonding metal layer, and the conductive layerBin the through holeH, so as to reach the conductive layerBand the conductive layerBon the second surfacewithout passing through the connection layerhaving a higher resistance. The total area of the conductive layerBdisposed in the display area is larger than the total area of the conductive layerBdisposed in the non-display area, so as to ensure that the current may be transmitted more evenly in the conductive layerB. Each of the light-emitting mesashas the same brightness when the same potential difference is applied thereto.

The micro light-emitting diode display devicein this embodiment further includes another conductive layerdisposed on the first surfaceof the connection layer. In other words, the conductive layeris disposed between the light-emitting mesas. The conductive layeris also configured to transmit the current from the circuit substrate C, and the insulating layeris disposed between the conductive layerand the light-emitting mesas.

Referring to, the micro light-emitting diode display deviceincludes a circuit substrate C, an epitaxy structure ESand a conductive layerC.

The epitaxy structure ESincludes a connection layerA and a plurality of light-emitting mesas. The connection layerA may be formed by epitaxial growth on a patterned epitaxial substrate, and includes a plurality of three-dimensional patternsP, wherein the three-dimensional patternsP are disposed on a second surfaceA. That is, the connection layerA is different from the connection layershown inin that the second surfaceof the connection layeris flat, and the second surfaceA of the connection layerA has a plurality of three-dimensional patternsP. The conductive layerC is disposed in a plurality of grooves G′ of the three-dimensional patternsP. In such a situation, the contact area between the conductive layersC disposed on the three-dimensional patternsP and the second surfaceA is larger than the contact area between the conductive layerand the second surfacein, improving the bonding yield between the connection layerA and the conductive layerC, and improving the transfer efficiency of the current from the circuit substrate C.

The conductive layer, the conductive layerA, the conductive layerB, and the conductive layerC described above are opaque conductive layers. However, the disclosure is not limited thereto. In some embodiments, the conductive layer, the conductive layerA, the conductive layerB, and the conductive layerC are transparent conductive layers.

Referring to, a micro light-emitting diode display deviceincludes a circuit substrate C, an epitaxy structure ES and a transparent conductive layerT. The transparent conductive layerT is disposed on the second surfaceof the connection layer, and completely covers the second surface. The material of the transparent conductive layerT may be an oxidized metal material such as indium tin oxide (ITO) or zinc oxide (ZnO). Since light can penetrate the transparent conductive layerT, it is not needed to expose a plurality of sub-areas of the second surface as the various opaque conductive layers do in the previous embodiments, such that the contact area between the transparent conductive layerT and the second surfaceis maximized, and the transfer efficiency of the current from the circuit substrate Cis greatly improved.

To sum up, in the micro light-emitting diode display devices provided by the embodiments of the disclosure, the conductive layer is disposed on the connection layer of the epitaxy structure. Since the resistance value of the conductive layer is less than the resistance value of the connection layer, the current from the circuit substrate may be transmitted within the conductive layer. In this case, even if the light-emitting mesas have different distances from the common ground point, the same potential difference may drive the same number of electron-hole pairs to recombine in those light-emitting mesas, which may avoid uneven brightness of the micro light-emitting diode display devices. In addition, in contrast with the case in which the conductive layer is disposed on the first surface of the connection layer, the fabrication process placing the conductive layer on the second surface of the connection layer has a significantly higher yield.